Abstract: The internal transcribed spacer regions (ITS) of the ribosomal RNA gene from 20 isolates of tobacco black shank were amplified with the polymerase chain reaction through the universal primers and sequence.The result showed that the total length of ITS of those 20 isolates tested were all 803bp, and the nucleotide sequence identity among those sequences was above 99.3%, and 20 strains had 99.6%-100% homologies with Phytophthora parasitica(GU111675.1) published in GenBank.But the ITS of those 20 isolates tested had some mutation sites which mainly concentrated in the ITS2 area and 468 mutation of isolates, which mainly came from Dechang and Xichang had certain regional.With the bio-software of MEGA6, Sequences from the above isolates were compared with 15 sequences published in GenBank database and phylogenitic trees were constructed based on ITS sequence data.The results showed that the isolates tested, GU111675.1, KF010303.1, AJ854295.1, KC768775.1 and L41383 were clustered into the same clade and all were Phytophthora parasitica (or Phytophthora nicotianae).They were clustered in a distant clade for different Phytophthora species and phylogenetically distinct each other.The results indicated that twenty isolates which isolated from different regions of Liangshan prefecture were Phytophthora parasitica.